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Key Insights | How Should Animal‑Experiment Samples Be Stored? What Precautions Should Be Taken When Shipping?

Many researchers are unfamiliar with the proper methods for preserving and shipping laboratory animal samples. Today, we’ll provide a comprehensive guide on how to store and transport these samples in a scientifically sound and efficient manner.

How should animal tissue samples be preserved?

To prevent cellular changes in tissue samples due to prolonged post‑explantation time, it is preferable to fix the samples within 20 minutes of removal to facilitate subsequent analyses. Note that submitted samples must be properly fixed, with a fixation period of at least two days. Different tissue samples and different analytical objectives require different fixation methods. The methods are also different.

Pathology test sample

1. Tissue sample

a. After in vitro washing, tissues should be fixed immediately; the fixative is typically 10% neutral buffered formalin or 4% paraformaldehyde (alcohol fixation is strongly discouraged), and samples should be stored at room temperature.

b. The container used for fixation must be selected according to the sample volume; the volume of the fixative should be 10–15 times that of the sample, and V‑bottomed, slender, or small tubes are not recommended for fixation. Large tissue specimens should be cut into sections before fixation to prevent autolysis and putrefaction in the central regions. If there are specific requirements, please choose alternative processing methods based on your experimental needs.

c. For frozen section specimens, the tissue must be fresh (processing steps: after removal, embed in OCT and store at −80°C. During transport, sufficient dry ice or ice packs must be provided).

d. Special tissues require specific fixatives to prevent sample alterations that could compromise subsequent analyses; refer to Table 1 for detailed requirements.

Table 1

e. Special care must be taken when handling the contents of the stomach and intestines: never squeeze them, as this can damage the mucosa. Instead, inject 10% neutral formalin or 4% paraformaldehyde into the stomach and cecum to fix the tissues for about half an hour. After that, make a longitudinal incision, rinse with 10% sodium chloride solution, and then proceed with further fixation.

f. For tissues such as skin and lung, which are relatively light and tend to float on the fixative: you may place a moistened cotton ball on top of the fixative to weigh it down, preventing the tissue from floating and ensuring adequate fixation. Alternatively, after the entire lung tissue has been excised, perfuse the main bronchus with fixative to flush the entire lung and fully distend it; then place the fully inflated lung in fixative for submission.

2. Cell samples

a. Adherent cells: After enzymatic digestion, centrifuge the cells, discard the culture medium while retaining the cell pellet, wash once with PBS, centrifuge again to remove the supernatant and retain the cell pellet, then resuspend in fixative (10% neutral buffered formalin or 4% paraformaldehyde) and send for analysis at room temperature.

b. Suspension cells: Centrifuge, discard the culture medium and retain the cell pellet; wash once with PBS, centrifuge again to remove the supernatant, and resuspend the cells in fixative (10% neutral-buffered formalin or 4% paraformaldehyde). Send for analysis at room temperature.

3. Electron microscopy samples

a. Obtain tissue samples measuring 2 mm × 2 mm, making them as thin as possible. If time does not permit trimming the tissue to the desired size, first fix the sample in the electron microscopy fixative for approximately 30 minutes; once the tissue has hardened, proceed with trimming and subsequent post‑fixation. Exceeding this time frame may prevent complete fixation, rendering subsequent experiments impossible; please give this step due attention.

b. During tissue sampling, aim to target the specific structures of interest as precisely as possible (e.g., collect renal cortex for glomerular analysis; obtain the pancreatic tail, which is rich in islets, for islet studies; for tissues such as skin or gastrointestinal mucosa that tend to curl in fixative, affix the specimen to filter paper before fixation).

c. Take care to avoid mechanical damage such as pinching with forceps, and ensure that blades are sharp to prevent tissue trauma.

d. Immediately after sectioning, immerse the specimen in electron microscopy fixative and fix at room temperature for 2 hours; then transfer it to 4°C for storage and transport using an ice pack. During storage and transport, ensure that the fixative is not allowed to freeze. At 4°C, the sample can be stored for approximately one month.

Biochemical assay sample

1. Blood sample

Select different blood anticoagulants based on the specific analytical parameters. All samples are stored at −80°C.

Biochemistry: It is recommended to prioritize serum, followed by heparin‑anticoagulated plasma.

ELISA: It is recommended to prioritize serum; if unavailable, use heparin- or EDTA‑anticoagulated plasma.

Coagulation assay: Only sodium citrate–anticoagulated plasma may be selected;

Complete blood count: Only EDTA-anticoagulated whole blood may be selected;

2. Tissue and cell samples

After ex vivo washing, tissue samples were flash-frozen in liquid nitrogen for 5 minutes and stored at −80°C. After cell sedimentation Store at −80°C.

How should animal tissue samples be shipped?

First, please ensure that the samples received are properly fixed and stored in accordance with the relevant sample‑preservation requirements.

a. Tissue samples fixed with fixative, tissue paraffin blocks, unstained slides, and other non-fluorescently stained slides should be shipped at room temperature. When packaging the slides, be sure to include paper towels or bubble wrap for shock protection.

b. Samples stored at 4°C should be shipped using ice packs, and the fixative must not be frozen during storage or transport.

c. Fluorescently stained slides: Place them in a slide box and ship under refrigerated, light‑protected conditions. You may insert tissue paper or bubble wrap inside the box for shock absorption, then wrap the exterior in aluminum foil to block light. Include an adequate amount of ice or dry ice to maintain low temperatures during transit.

d. During the transport of frozen section samples, sufficient dry ice must be provided, and an insulated foam box should be used for packaging.

e. Submitted specimens must include information on the species, specimen type, time of tissue excision, fixation time, fixation method, and tissue site. This information must be consistent with and clearly legible on the accompanying paper documentation, and it must be confirmed that the tissue has been fully fixed. If uncertain, please contact the pathology laboratory staff for guidance.

f. Tissue samples that are too small or too thin are prone to loss and are not recommended for submission (e.g., samples with a thickness of less than 1 mm).

The editor has compiled a table for easy saving (Table 2).

What is the sample shipment volume?

If omics‑related assays are required, attention should be paid to sample handling and the recommended sample volume. We have compiled this information in a table for easy record‑keeping (see Table 3‑4).